Commercially available fiber optic data transfer systems have, in recent years, significantly increased the speed at which information can be transferred from point to point. Electro-optic (EO) light modulators, that operate at a wavelength .lambda. of approximately 1.5 .mu.m with bandwidths of 2.5 and 10 GHz, are vital to these data transfer systems. The resulting 10 Gbit/sec data transfer rate is a well entrenched (although recently entrenched) technological standard in present-day communications systems. Communication industries have already identified 40 Gbit/sec as the next-generation target for data transfer systems. The industry's hope is to operate these modulators with drive voltages of approximately 2 to 5 V. Device insertion loss must also be less than approximately 6 dB. The target date for these new standards is early in the 21st century, however, industrial research efforts are presently under way to study potential technologies to achieve these goals.
Commercially available EO modulators are currently based on integrated optic waveguide elements fabricated in bulk LiNbO.sub.3 crystals. The maturity and proven long-term stability of commercial LiNbO.sub.3 modulators has established this technology without competition in optical communications markets (for example, cable TV and telecommunications). However, existing fiber optic networks are capable of operating at much higher bandwidths than provided by the available LiNbO.sub.3 modulators. A current limiting aspect of data transfer rates in fiber optic-based communications is the operation bandwidth of the commercially available LiNbO.sub.3 electro-optic modulators.
It has been shown that the bandwidth of LiNbO.sub.3 EO modulators can be significantly improved by using a composite substrate for the device host. The key to bandwidth improvement is a reduction in the effective dielectric constant of the composite substrate over that of bulk substrates. Most demonstrated composite substrate devices have been realized in the form of bulk grown LiNbO.sub.3 coated with a lower dielectric buffer layer. A second proposed composite substrate is that of a thin film ferroelectric on top of a low dielectric substrate. The major obstacle to the practical application of thin film ferroelectrics has been the difficulty encountered in fabricating high quality films.
Current commercial electro-optic modulators are based on devices fabricated in bulk-grown LiNbO.sub.3 crystals. Many research groups are focussing on thin film ferroelectric materials grown by a number of techniques (e.g., metal-organic chemical vapor deposition, molecular beam epitaxy, pulsed laser deposition, and sputtering). However, these growth techniques are new to the application of thin film ferroelectric growth. Thus, a need exists in the industry for a manufacturable modulator capable of meeting the needs of the next generation of communications systems.